Railroads are typically constructed to include a pair of elongated, substantially parallel rails, which are coupled to a plurality of laterally extending rail ties. The rail ties are disposed on a ballast bed of hard particulate material such as gravel and are used to support the rails. Over time, normal wear and tear on the railroad may cause the rails to deviate from a desired profile based on movement of the underlying ballast, and as such voids or gaps under the rail ties may appear.
The traditional method of fixing voids that appeared under rail ties was very labor and time intensive, as it required measurement of the voids under each individual rail tie, manually lifting the rail ties, and then spreading a pre-measured quantity of ballast under the rail ties to raise the rails. In the 1970s, British Rail developed a mechanization of the traditional method by modifying a tamper and installing a system for distributing ballast under the rail tie with blasts of compressed air, creating the first stoneblower.
Modern stoneblowers are typically wheeled cars that comprise a track lifting device, a supply of crushed ballast rock, a source of compressed air, and a number of workheads. Each workhead carries a pair of blowing tubes. In operation, the track lifting device raises the track rails and the underlying rail ties to which the rails are secured. The workhead forces the blowing tubes into the ballast adjacent the raised rail ties with each pair of blowing tubes straddling a track rail. Stone is then blown through the blowing tubes into the voids beneath the raised rail ties. The workhead withdraws the blowing tubes and the track rail and rail ties are lowered. The stoneblower then advances to the next set of rail ties and repeats this procedure.
Modern stoneblowers are designed to restore a track's vertical and lateral alignment to an accuracy of 1.0 mm without disturbing the pre-existing compacted ballast layer. Vehicle bogies allow stoneblowers to measure a loaded track profile, and therefore measure the voids in the ballast under each rail tie. Computers then calculate the quantity of ballast to be “blown” under each rail tie, thus minimizing stone usage based on the track category or speed limit.
Compared with tamping, stoneblowers advantageously can be used on high speed track lines, treat only the areas of the track that need treatment, and reduce ballast damage. Further, after stoneblowing, the track does not become more rigid because the stoneblower only treats areas that need treatment, while the majority of the rail ties are supported on the original ballast and railroad bed. In addition, a new rock supplier is not needed to use a stoneblower for track maintenance. The injected ballast often comes from the same quarries and has the same attrition values as normal ballast. Additionally, using small, crushed stones as ballast causes less damage to the underside of the rail ties because the small stone is less likely to fail under heavy axle load based on increased surface area.
Current stoneblowers have some drawbacks, however, based on the current design incorporating pairs of parallel blowing tubes. For example, modern stoneblowers cannot efficiently blow ballast under non-uniform sections of rails, such as at railroad frogs or crossings, because the pairs of blowing tubes are only configured to have blowing tubes on each side of a rail and/or on each side of a rail tie, but they cannot blow ballast directly under the frog and/or under the rail tie area directly under the frog. However, in the continually changing world of track maintenance, it is essential that rail companies be able to provide quality track maintenance and alignment equipment that can service all sections of rail, not just uniform sections of rail. Moreover, conventional stoneblowers are large vehicles that are expensive to manufacture, deploy and operate. Smaller stoneblower machines, including those that can be deployed to work small areas of rail, such as frogs, are needed. Therefore, an improved stoneblower is desired.